Determinism and reproducibility are related closely enough to blur together, but they answer different questions. Determinism is about the system: does the same run produce the same output, every time. Reproducibility is about what that property is actually worth — can someone else, on their own machine, at a later date, regenerate the exact same result and check it for themselves.
The gap between "it's deterministic" and "it's reproducible"
A system can be perfectly deterministic and still fail to be reproducible in practice, if the specific inputs that produced a result — the exact data, the exact configuration, the exact seed — aren't preserved anywhere alongside it. Determinism is necessary for reproducibility, but it isn't sufficient on its own; reproducibility also requires that everything needed to regenerate the result is actually captured and shared, not just theoretically possible to recreate if someone happened to still have all the pieces.
What this looks like in practice
A saved result that carries its own execution config, its own data references, and its own seed is something a colleague can open and verify independently — not by trusting a description of what happened, but by regenerating exactly what happened and comparing it directly. The same applies across time as much as across people: a result revisited six months later, with the specifics of that day's reasoning long forgotten, can still be checked against its own record rather than relying on a memory of why it seemed convincing at the time.
Why "trust me" is the thing this replaces
Without reproducibility, a result's credibility rests on the person presenting it — their care, their honesty, their memory of what they actually did. With it, credibility rests on something checkable: the same inputs, run again, either produce the same output or they don't. That shift, from trusting a person's account to verifying a result directly, is most of what separates a claim from evidence, and it's only available to a research process that treats reproducibility as something to actively preserve, not just a property that determinism happens to make possible.
Full reference: docs · The execution model this rests on: execution specification · The workflow this maps onto: reamerlabs.com